A display apparatus configured to display an image, which is stereoscopically perceived, alternately shows a left image for a left eye and a right image for a right eye in a given cycle (e.g., a field cycle). The displayed left and right images contain different contents from each other by parallax. A viewer views the left and right images by means of an eyeglass device, which has liquid-crystal shutters driven in synchronism with the display cycle of the left and right images (cf., Patent Documents 1 and 2). As a result, the viewer may perceive a stereoscopic object depicted in the left and right images.
FIG. 12 is a block diagram of a conventional image viewing system. The image viewing system shown in FIG. 12 receives an input of a 60-Hz image signal (left and right image signals).
An image viewing system 900 comprises an image signal processor 901 configured to receive an input of a 60-Hz image signal (left and right image signals). The image signal processor 901 converts the input image signal into 120-Hz left and right image signals. The left and right image signals obtained as a result of the conversion are output to a liquid crystal driver 902 and a backlight source controller 903. The liquid crystal driver 902 converts the 120-Hz left and right image signals according to a display format of a liquid crystal panel 904. The left and right image signals converted by the liquid crystal driver 902 are output to the liquid crystal panel 904. The backlight source controller 903 outputs an emission control signal to a backlight source 905. The backlight source 905 emits light to the liquid crystal panel 904 from its back surface in response to the emission control signal. Therefore, left and right images are alternately displayed at 120 Hz on the liquid crystal panel 904.
An eyeglass device 950 has a left shutter 951 and a right shutter 952. A shutter control circuit 906 for the left shutter 951 and a shutter control circuit 907 for the right shutter 952 synchronously control the left and right shutters 951, 952 in response to the 120-Hz left and right image signals converted by the image signal processor 901.
FIG. 13 is a control timing chart of the conventional image viewing system 900. Section (A) of FIG. 13 shows scan timing for scanning the left and right images on the liquid crystal panel 904. Section (B) of FIG. 13 shows timing for brightening the backlight source 905. Section (C) of FIG. 13 shows timing for opening/closing the shutters 951, 952 of the eyeglass device 950. The conventional image viewing system 900 is described with reference to FIGS. 12 and 13.
The left and right image signals are sequentially written into the liquid crystal panel 904. Meanwhile, the backlight source 905 is brightened all the time. The shutter control circuits 906, 907 control the shutters 951, 952. After the right-and-left alternate write-scanning on the liquid crystal panel 904, the shutters 951, 952 are opened/closed under the control of the shutter control circuits 906, 907 so that an open period of each shutter becomes half of each image period. The left and right images are viewed with the right and left eyes of the viewer through the shutters 951, 952. Therefore, the viewer may create a visually stereoscopic image in the brain.
In the image viewing system, which is operated under the control timing shown in FIG. 13, the viewer views only one of the left and right images while one of the shutters 951, 952 are opened (an image viewing period long enough to create a stereoscopic image). On the other hand, the backlight source 905 is brightened all the times even in another period than the opening periods of the shutters 951, 952. Therefore, the image viewing system, which is operated under the control timing shown in FIG. 13, is not preferable in terms of saving electricity.
FIG. 14 is another control timing chart of the conventional image viewing system 900. Section (A) of FIG. 14 shows scan timing for scanning the left and right images on the liquid crystal panel 904. Section (B) of FIG. 14 shows timing for brightening the backlight source 905. Section (C) of FIG. 14 shows timing for opening/closing the shutters 951, 952 of the eyeglass device 950. The conventional image viewing system 900 is further described with reference to FIGS. 12 to 14.
Patent Document 2 discloses control to turn on the backlight source 905 only while the left or right image is viewed. Unlike the control shown in FIG. 13, under the control shown in FIG. 14, the backlight source 905 emits the light only while the left or right image is viewed. Therefore, the control shown in FIG. 14 is better than the control shown in FIG. 13 in terms of saving electricity.
The image viewing system shown in FIG. 14 has the following problems. The fact that the backlight source 905 is turned on only while the left or right image is viewed means a shortened lighting period to turn on the backlight source 905. A temperature of the liquid crystal panel goes down under the shortened lighting period of the backlight source 905. The decrease in temperature of the liquid crystal panel 904 reduces a response speed of the liquid crystal panel 904.
If the response speed of the liquid crystal panel 904 goes down, for example, the left image may be still partially displayed on the liquid crystal panel 904 even after completion of the right image scanning because of a delayed response of liquid crystal. As a result, image light from the left image travels through the right shutter and reaches the right eye of the viewer. Likewise, the image light from a part of the right image, which is still displayed after completion of the left image scanning, travels through the left shutter and reaches the left eye of the viewer. The left image viewed with the right eye and/or the right image viewed with the left eye are obstruction images called “crosstalk”, which interferes with the creation of the visually stereoscopic image in the brain of the viewer.
Patent Document 1: JP 62-133891 A
Patent Document 2: JP 2009-25436 A